| 2020-05-22 |
hst_0795.pmap |
operational |
These WFC3 UVIS superdarks, drk, and CTE corrected superdarks, dkc, will affect all UVIS data taken from April 16th through May 16th 2020. Currently, the automated calibration pipeline and Calibration Reference Data System only have WFC3 UVIS drk and dkc reference files up to a USEAFTER date of April 14th 2020. The automated pipeline should now use these reference files to perform dark subtraction on any UVIS datasets obtained between the dates above because they represent the most accurate estimate of the dark current and hot pixels at the time of the science observation. These WFC3 UVIS drk and dkc files were generated using dark exposures from the HST Cycle 27 daily monitoring programs 15715 and 15712. More information regarding the method used to create UVIS dark calibration reference files can be found in WFC3 ISR 2016 08. Additionally, the header of each reference file has a detailed history section outlining the process and provides a list of datasets used to create each file. |
| 2020-05-21 |
hst_0794.pmap |
archived |
Intrinsic excess thermal energy trapped in the silicon lattice of the Wide Field Camera 3, WFC3, ultraviolet-visible, UVIS, detector, known as dark current, is typically removed from science observations using UVIS dark calibration reference files. However, this dark current can be used as a means to characterize a pixels behavior and determine whether the pixel varies excessively over time compared to its expected noise. We use a novel data structure known as a pixel history image to efficiently evaluate each WFC3/UVIS pixel over time. We find that the vast majority of hot pixels, about 8 percent of the detector in 2018, are in fact quite stable and as such, can be calibrated. A small portion of pixels, less than 1 percent, are genuinely unstable and should not be used. To encode this distinction in the UVIS bad pixel reference files, we employ a data quality flag, 32, to mark the unstable pixels identified in this study. Hot pixels continue to be assigned the usual data quality flag, 16. With the additional data quality flag, WFC3/UVIS users will have enhanced control over which pixels to include, and which to exclude, in their analyses. This new bad pixel table was generated using the most recent complete anneal period, and therefore accurately captures the most current bad pixel map of the UVIS detector. More information about the UVIS bad pixel tables is outlined in the WFC3 ISR 2018.15 |